Ventricular fibrillation/arrhythmia and asphyxia account for a significant percentage of cardiac arrests. The course of a cardiac arrest, neurological deficit and myocardial dysfunction differs between these two causes of cardiac arrest. For example, asphyxia cardiac arrest is characterized by a progressive clinical decline in cardiac function initiated by hypoxemia, hypercarbia, acidosis, hypotension and subsequent cessation of cardiac activity. Cardiac mitochondrial damage may be greater and occur more quickly with asphyxia cardiac arrest as compared to arrhythmia arrest. It is clinically valuable to be able to ascertain the cause of cardiac arrest so that an appropriate clinical response may be employed. For example, in many cases, an arrhythmic arrest may be treated by shocking the patient with a defibrillator, whereas an asphyxia arrest may be treated by shocking the patient with a defibrillator and by utilizing a ventilator.
Particularizing the treatment protocol to the patient “down time” or cardiac arrest phase of the patient can improve outcomes. See, for example, “Minimally Interrupted Cardiac Resuscitation by Emergency Medical Services for Out-of-Hospital Cardiac Arrest,” Bobrow, Bentley J., M.D., et al., Journal of the American Medical Association, vol. 299, no. 10, Mar. 12, 2008, pp. 1158-1165, which is incorporated by reference herein. Previously it has been suggested that ventilator support or active ventilation may be delayed for several minutes or more in cardiac resuscitation treatment protocol. However, contrary to this suggestion, for cardiac arrest caused by asphyxia, sooner and/or more active ventilation treatment may be beneficial.
Also, a three-phase time-sensitive model for resuscitation after cardiac arrest has been described in the literature to include the following: the electrical phase, the circulatory phase, and the metabolic phase. See, e.g., “Resuscitation After Cardiac Arrest,” Weisfeldt, Myron L., M.D., et al., Journal of the American Medical Association, vol. 288, no. 23, Dec. 18, 2002, pp. 3035-3038, incorporated by reference herein. Different treatment protocols may be indicated for different phases of resuscitation, and the phases may be identified (or at least estimated) based on the duration of time from the onset of the cardiac arrest, referred to as “downtime.” It would also be preferable to further distinguish between cardiac arrest caused by ventricular fibrillation/arrhythmia and asphyxia to determine the treatment protocol.